Prior to 1998, most vehicles sold in the United States included a two-piece wheel bearing system that attached each tire/wheel combo to the vehicle. This unit included a hub assembly and wheel bearings inside the assembly that allows the tires and wheels to spin freely on the vehicle. Inside the bearing is a wheel seal that is designed to keep the bearings properly lubricated and free of debris, dirt and other materials from the bearings.
Wheel seals and bearings for cars built before 1998 are recommended to be serviced every 30,000 miles. This service commonly includes removing the wheel seal and bearing from each hub, cleaning them, packing them with grease, and replacing any damaged seals. However, most car owners in the United States that have vehicles built in 1997 or earlier don't have this important routine maintenance completed. As a result, the potential of having a broken or failing wheel seal is higher. If this part is wearing out, it will cause damage to the wheel bearings and will typically display a few warning signs that indicate the bearing is wearing out or failing.
Listed below are a few of the common symptoms of a bad of failing wheel seal.
1. Grease is leaking from the bearings
The wheel seal is supposed to fit very tight in the wheel assembly and protects the wheel bearings from dirt, water, and other debris that can cause damage. Inside the wheel bearing is a tremendous amount of grease that keeps the bearings running smooth, cool and free. However, when the wheel seal is loose, the grease can and often does escape from the wheel bearing. As the wheels turn, centripetal force will fling this grease around the wheel hub and can leak onto the ground. If you notice that there is grease or what appears to be hard dirt near the tires of your car, this could be a warning sign of a worn or broken wheel seal and should be inspected by a professional mechanic as soon as possible.
If a wheel seal is damaged or falls off, it will damage the wheel bearings as well rather quickly, so it's vital to have this fixed as soon as possible. However this symptom may also indicate a torn CV boot which does a similar job as the wheel bearing seal. In either case, it's something that should be fixed sooner rather than later.
2. Visible damage to the wheel seal
This symptom is hard for most car owners to recognize, but is easy for mechanics that complete tire, suspension or brake service. From time to time, the wheel seal will be hit by potholes, items under the car or debris in the road. When this happens, it can hit the wheel seal housing and cause the seal to break or put a dent in the wheel seal. This can also be seen while having the oil changed by a technician. If you are told by a mechanic or technician that is completing maintenance under your vehicle that they notice the wheel seal is damaged, make sure you ask them to replace the seal and inspect the wheel bearings. In many cases the damaged wheel seal can be replaced and the bearings serviced with new grease and cleaned if caught early enough.
3. Noises coming from the tires and wheels
As indicated above, when a wheel seal is bad, broken, or has come off, the wheel bearings are quickly damaged as well. When the wheel bearing is losing lubrication, the metal of the bearing will grind against the metal of the wheel hub. This will sound like a roar or grinding noise and will increase in volume and pitch as the vehicle accelerates.
As with any of these symptoms or warning signs of a bad of failing wheel seal, contact a local ASE certified mechanic so they can service, inspect, and diagnose the problem quickly. A good rule of thumb to remember is to have your wheel bearings inspected and serviced every 30,000 miles or during every brake job. This is especially critical on front wheel drive vehicles, but should also include the rear axle as well. By being proactive about wheel bearing maintenance you can avoid some expensive damage to wheel bearings and other wheel hub components, but also reduce the potential of having an accident.